This invention relates to open-celled, flexible polyurethane foams and to a process for their production.
Open-celled polyurethane foams and their use in the production of plastics are described in German Offenlegungsschriften 29 28 357 and 25 24 834. However, the plastics produced from these disclosed foams are totally different from plastics produced from flexible polyurethane foams. High-density and elastomeric plastics are obtained from open-celled polyurethane foams. The use of compounds such as those employed in the practice of the present invention to produce open-celled flexible foams and the advantages achieved are not taught or suggested by the prior art.
An important feature of the present invention is the use of dicarbonic acid alkyl, cycloalkyl or benzyl esters in combination with water. This feature of the invention eliminates the need to use fluorinated and chlorinated hydrocarbons (CFC's), which are regarded as ecologically harmful, in the production of, for example molded foams.
Until now, CFC's have been used for two reasons: (1) They act as an additional physical blowing agent and thereby promote reduction of the density of foams which in turn reduces raw material costs for the processor; and (2) they do not form any hardness-increasing urea segments (from the isocyanate/water reaction) in the foaming process so the hardness of foams is reduced. The simple production of flexible foams has therefore been believed to be possible only when CFC's are used.
Both of the above-enumerated factors must be given adequate consideration in the search for new substitutes for CFC's. These factors have not however been sufficiently addressed in the CFC-free processes which have been proposed in the past.
For example, it is known that foam density can be reduced by increasing the quantity of water used in a raw material formulation. The quality of the foams produced with such larger amounts of water is however significantly reduced. Known measures which have successfully reduced foam hardness have not however been able to reduce density.
It would therefore be advantageous to have a process for producing high quality, elastic, low density foams in which no CFC was employed.